Search Results (124)

Space-based optical imaging detection serves as a crucial means for acquiring characteristic information of space objects, with the quality and resolution of images directly influencing the accuracy of subsequent missions. Addressing the scarcity of datasets in space-based optical imaging, this study introduces a method that combines an improved Phong model and higher-order spherical harmonics (HOSH) for the optical imaging computation of space objects. Utilizing HOSH to fit the light field distribution, this approach comprehensively considers direct sunlight, earthshine, reflected light from other extremely distant celestial bodies, and multiple scattering from object surfaces. Through spectral reflectance experiments, an improved Phong model is developed to calculate the optical scattering characteristics of space objects and to retrieve common material properties such as metallicity, roughness, index of refraction (IOR), and Alpha for four types of satellite surfaces. Additionally, this study designs two sampling methods: a random sampling based on the spherical Fibonacci function (RSSF) and a sequential frame sampling based on predefined trajectories (SSPT). Through numerical analysis of the geometric and radiative rendering pipeline, this method simulates multiple scenarios under both high-resolution and wide-field-of-view operational modes across a range of relative distances. Simulation results validate the effectiveness of the proposed approach, with average rendering speeds of 2.86 s per frame and 1.67 s per frame for the two methods, respectively, demonstrating the capability for real-time rapid imaging while maintaining low computational resource consumption. The data simulation process spans six distinct relative distance intervals, ensuring that multi-scale images retain substantial textural features and are accompanied by attitude labels, thereby providing robust support for algorithms aimed at space object attitude estimation, and 3D reconstruction. Full article

This study proposes a couple of analytical solutions that characterize the anisotropic dense celestial bodies within the Rastall-Rainbow theoretical framework. The analysis assumes a static spherically symmetric matter distribution and derives the corresponding modified field equations. By utilizing well-established radial metric functions and merging them with the two principal pressures, we obtain differential equations related to the time component. Subsequently, we perform the integration of these equations to determine the remaining geometric quantity that encompasses various integration constants. The proposed interior solutions are then matched with the Schwarzschild exterior metric at the boundary of the compact object, facilitating the determination of the constants. Additionally, the incorporation of the non-minimal coupling parameter into these constants is accomplished by enforcing the null radial pressure at the boundary. Afterwards, we rigorously examine the physical characteristics and critical stability conditions of the formulated models under observational data from two pulsars, say 4U 1820-30 and LMC X-4. It is concluded that our models are well-aligned with essential criteria required to ensure the physical viability of stellar structures, subject to specific parametric values. Full article

Deep space exploration missions face technical challenges such as long-distance communication delays and high-precision autonomous positioning. Traditional ground-based telemetry and control as well as inertial navigation schemes struggle to meet mission requirements in the complex environment of deep space. As a vision-based autonomous navigation technology, image-based navigation enables spacecraft to obtain real-time images of the target celestial body surface through a variety of onboard remote sensing devices, and it achieves high-precision positioning using stable terrain features, demonstrating good autonomy and adaptability. Craters, due to their stable geometry and wide distribution, serve as one of the most important terrain features in deep space image-based navigation and have been widely adopted in practical missions. This paper systematically reviews the research progress of deep space image-based navigation technology, with a focus on the main sources of remote sensing data and a comprehensive summary of its typical applications in lunar, Martian, and asteroid exploration missions. Focusing on key technologies in image-based navigation, this paper analyzes core methods such as surface feature detection, including the accurate identification and localization of craters as critical terrain features in deep space exploration. On this basis, the paper further discusses possible future directions of image-based navigation technology in response to key challenges such as the scarcity of remote sensing data, limited computing resources, and environmental noise in deep space, including the intelligent evolution of image navigation systems, enhanced perception robustness in complex environments, hardware evolution of autonomous navigation systems, and cross-mission adaptability and multi-body generalization, providing a reference for subsequent research and engineering practice. Full article

Star trackers are critical electro-optical devices used for satellite attitude determination, typically tested using Optical Ground Support Equipment (OGSE). Within the POR FESR 2014–2020 program (funded by Regione Toscana), we developed MINISTAR, a compact electro-optical prototype designed to generate synthetic star fields in apparent motion for realistic ground-based testing of star trackers. MINISTAR supports simultaneous testing of up to three units, assessing optical, electronic, and on-board software performance. Its reduced size and weight allow for direct integration on the satellite platform, enabling testing in assembled configurations. The system can simulate bright celestial bodies (Sun, Earth, Moon), user-defined objects, and disturbances such as cosmic rays and stray light. Radiometric and geometric calibrations were successfully validated in laboratory conditions. Under the PR FESR TOSCANA 2021–2027 initiative (also funded by Regione Toscana), the concept was further developed into STARLITE (STAR tracker LIght Test Equipment), a next-generation OGSE with a higher Technology Readiness Level (TRL). Based largely on commercial off-the-shelf (COTS) components, STARLITE targets commercial maturity and enhanced functionality, meeting the increasing demand for compact, high-fidelity OGSE systems for pre-launch verification of attitude sensors. This paper describes the working principles of a generic system, as well as its main characteristics and the early advancements enabling the transition from the initial MINISTAR prototype to the next-generation STARLITE system. Full article

This paper aims to present a set of possible transfer trajectories for a rendezvous mission with asteroid 2024 YR4, using a spacecraft propelled by a photonic solar sail. Asteroid 2024 YR4 was discovered in late December 2024 and was briefly classified as Torino Scale 3 for three weeks in early 2025, before being downgraded to zero at the end of February. In this study, rapid Earth-to-asteroid transfers are analyzed by solving a typical optimal control problem, in which the thrust vector generated by the solar sail is modeled using the optical force approach. Numerical simulations are carried out assuming a low-to-medium performance solar sail, considering both a simplified orbit-to-orbit transfer and a more accurate scenario that incorporates the actual ephemerides of the celestial bodies. The numerical results indicate that a medium-performance solar sail can reach asteroid 2024 YR4, achieving the global minimum flight time and arriving before its perihelion passage in late December 2032. Full article

Deep space Color Remote Sensing Images (DCRSIs) are of great significance in reconstructing the three-dimensional appearance of celestial bodies. Among them, deep space color restoration, as a means to ensure the authenticity of deep space image colors, has significant research value. The existing deep space color restoration methods have gradually evolved into a joint restoration mode that integrates color images and spectrometers to overcome the limitations of on-orbit calibration plates; however, there is limited research on theoretical models for this type of method. Therefore, this article begins with the physical process of deep space color imaging, gradually establishes a color imaging spectral model, and proposes a new color restoration method for the color restoration of Mars remote sensing images. The experiment verifies that our proposed method can significantly reduce color deviation, achieving an average of 8.43 CIE DE 2000 color deviation units, a decrease of 2.63 (23.78%) compared to the least squares method. The color deviation decreased by 21.47 (71.81%) compared to before restoration. Hence, our method can improve the accuracy of color restoration of DCRSIs in space orbit. Full article

Multi-tethered spacecraft formation refers to a group of spacecraft that are connected by tethers. These spacecraft work together to perform tasks, such as encircling and capturing small celestial bodies. When the multi-tethered spacecraft formation is in the process of encircling and capturing small celestial bodies, there is a significant risk of the tethers colliding with the soil (or surface material) of the small celestial body. Such a collision can affect the trajectory of the small celestial body detector. To address this issue, a coupled dynamic model has been proposed. This model takes the interaction between the tethers and the soil of the small celestial body into account. The discrete element method is used to establish the asteroid soil model, and the multi-body-tethered spacecraft system is simplified into a two-spacecraft system. The detector model is established by using the dual quaternion, and the tether model is established by using the chain rod model combined with the finite element method. Finally, a multi-condition simulation test is carried out. The results show that the influence of tether–soil coupling on the trajectory of the detector is mainly as follows: the influence of tether–soil interaction on the trajectory of the detector is mainly reflected in the displacement of the detector along the axial direction of the tether. Full article

The determination of the shape of the Earth has been one of the fundamental problems geodesy was supposed to solve; it has been and possibly still is the main geodetic problem. It is thus appropriate for geodesists to look at this problem periodically, and this is what the authors of this paper aim to do. About 50 years ago, geodesists started using satellites as a new and very powerful tool. Many problems that were either impossible to solve or that presented almost unsurmountable hurdles to solutions have now been solved relatively simply, so much so that in the eyes of some people, satellites can solve all geodetic problems, and attempts are being made to show that this is indeed the case. We feel that the time has come to show that even satellites have their limitations, the main one being that for them to remain in their orbit, they must fly quite high, typically at several hundred kilometres. The gravitational field of the Earth (and that of any celestial body) smoother as one gets higher and higher. In other words, the gravitational field at the satellite orbit altitude loses detailed information that one can see at the surface of the Earth. In this contribution, we shall try to explain what satellites have contributed to the study of the shape of the Earth and what issues remain to be sorted out. Full article

The polemics of idol worship in John Capgrave’s Life of Saint Katherine of Alexandria have been interpreted by previous scholars as either the author’s engagement with the Lollard image controversy or a political critique of Henry VI. This essay, however, shifts the focus from Katherine and her iconoclasm to the concept of divine iconoclasm, defined here not only as the divinely sanctioned or divinely motivated destruction of religious images but also as God’s direct intervention to dismantle false representations and correct human perceptions of the divine. It further argues that Capgrave’s Life redefines sacred space as primarily constructed through light, emphasizing its immateriality and exposing the saint’s physical limitations. In these scenarios, divine iconoclasm emerges as a constructive force that resolves the tension between the secular and the sacred. Moreover, Christ’s celestial manipulation of the vision of sacred space and the relationship between body and space—encouraging confidence while discouraging self-inflation—serves as a model for how a monarch should inspire both love and fear. In this way, Capgrave’s Mirrors for Princes is embedded within his hagiography, where the image debate features prominently, addressing the heated political and theological controversies of his time. By combining these elements, the essay bridges two strands of criticism that have previously treated the political and theological dimensions of the text separately. Full article

With the advancement of space exploration, the development of sustainable construction technologies has become essential for the establishment of enduring extraterrestrial habitats. In Situ Resource Utilization (ISRU) assumes a pivotal role by facilitating the use of indigenous materials on celestial bodies such as the Moon and Mars, thereby reducing reliance on terrestrial resources. This review provides a comprehensive analysis of the latest ISRU-based construction technologies, with particular emphasis on biocementation techniques. It further examines the challenges associated with the application of biocementation in extreme space environments and outlines prospective research directions. The continued advancement of ISRU technologies through interdisciplinary collaboration remains crucial for the realization of viable and cost-efficient extraterrestrial construction solutions. Full article

This study presents an improved methodology for celestial triangulation optimization in spacecraft navigation, addressing limitations in existing approaches. While current methods like Linear Optimal Sine Triangulation (LOST) provide statistically optimal solutions for position estimation using multiple celestial body observations, their performance can be compromised by suboptimal measurement pair selection. The proposed approach, called the Improved-LOST algorithm, introduces a systematic method for evaluating and selecting optimal measurement pairs based on a Cramér–Rao Lower-Bound (CRLB) analysis. Through theoretical analysis and numerical simulations on translunar trajectories, this study demonstrates that geometric configuration significantly influences position estimation accuracy, with error variances varying by orders of magnitude depending on observation geometry. The improved algorithm outperforms conventional implementations, particularly in scenarios with challenging geometric configurations. Simulation results along a translunar trajectory using various celestial body combinations show that the systematic selection of measurement pairs based on CRLB minimization leads to enhanced estimation accuracy compared to arbitrary pair selection. The findings provide valuable insights for autonomous navigation system design and mission planning, offering a quantitative framework for assessing and optimizing celestial triangulation performance in deep space missions. Full article

Space trajectory planning is a complex combinatorial problem that requires selecting discrete sequences of celestial bodies while simultaneously optimizing continuous transfer parameters. Traditional optimization methods struggle with the increasing computational complexity as the number of possible targets grows. This paper presents a novel reinforcement-learning algorithm, inspired by AlphaZero, designed to handle hybrid discrete–continuous action spaces without relying on discretization. The proposed framework integrates Monte Carlo Tree Search with a neural network to efficiently explore and optimize space trajectories. While developed for space trajectory planning, the algorithm is broadly applicable to any problem involving hybrid action spaces. Applied to the Global Trajectory Optimization Competition XI problem, the method achieves competitive performance, surpassing state-of-the-art results despite limited computational resources. These results highlight the potential of reinforcement learning for autonomous space mission planning, offering a scalable and cost-effective alternative to traditional trajectory optimization techniques. Notably, all experiments were conducted on a single workstation, demonstrating the feasibility of reinforcement learning for practical mission planning. Moreover, the self-play approach used in training suggests that even stronger solutions could be achieved with increased computational resources. Full article

While Kepler is regarded as a major figure in standard historical accounts of the scientific revolution of early modern Europe, he is typically seen as having one foot in the new scientific culture and one in the old. In some of his work, Kepler appears, along with Galileo, to be on a trajectory towards Newton’s celestial mechanics. In addition to his advocacy of Copernicus’s heliocentrism, he appealed to physical causes in his explanations of the movements of celestial bodies. But other work appears to express a neo-Platonic “metaphysics” or “mysticism”, as most obvious in his embrace of the ancient tradition of the “music of the spheres”. Here I problematize this distinction. The musical features of Kepler’s purported neo-Platonic “metaphysics”, I argue, was also tied to Platonic and neo-Platonic features of the methodology of a tradition of mathematical astronomy that would remain largely untouched by his shift to heliocentrism and that would be essential to his actual scientific practice. Importantly, certain features of the geometric practices he inherited—ones later formalized as “projective geometry”—would also carry those “harmonic” structures expressed in the thesis of the music of the spheres. Full article

A vision-aided autonomous navigation system for translunar missions based on celestial triangulation (Earth and Moon) is proposed. Line-of-Sight (LoS) vectors from the spacecraft to celestial bodies, retrieved using ephemeris data from the designed translunar trajectory, are used to simulate camera observations at unknown locations. The resection problem of triangulation is employed to calculate the relative position of the spacecraft with respect to the observed bodies along the trajectory. The noisy LoS data are processed using the Extended Kalman Filter (EKF). Simulation results demonstrate that, starting from a random initial location, the proposed navigation system can be used for navigating translunar trajectories with the fast and accurate algorithm employed. Full article